The present invention relates to a transmission for an automotive vehicle, and in particular relates to an automatic type transmission particularly suitable for use in a transverse front engine front wheel drive type automotive vehicle, or a so called FF vehicle.
There is a known type of front engine front wheel drive type automotive vehicle in which the internal combustion engine thereof is mounted transversely to the vehicle body, with its crankshaft extending at right angles to the longitudinal axis of the automotive vehicle body, i.e. parallel to the front axle line of the vehicle, and in which the automotic transmission thereof is attached to the internal combustion engine with the directions of the rotational axes of the various mechanisms contained therein likewise extending transversely to the longitudinal axis of the vehicle body. In such a transverse type of construction, it is very important to keep the axial length of the automatic transmission as short as possible, so as to fit the transmission mechanism and the rotary power train of the vehicle as a whole into the shortest possible space, in view of the severe restriction imposed on the axial length of this rotary power train by the overall width of the vehicle, within which of course the rotary power train must be accomodated.
As a transverse type automatic transmission of the abovementioned kine and improved with respect to its shortness in axial length, there has been proposed in U.S. patent application Ser. No. 418,026, filed on Sept. 14, 1982, and entitled "Transverse type automatic transmission with through lay shaft" an automatic transmission which includes a fluid torque converter and a first and a second gear transmission mechanism each of which has two coaxial drive members--a power input member and a power output member--and is selectable to any one of several speed ratios, wherein: rotational power is outputted from the fluid torque converter to the first gear transmission mechanism; the torque converter, and the first gear transmission mechanism including the power input and the power output members thereof, are all coaxial on a first axis; a through lay shaft extends along a second axis parallel to the first axis, and passes through the second gear transmission mechanism, whose power input and output members are also coaxial on the second axis, so as to support these; and a rotational power transfer mechanism transfers rotational power between the power output member of the first gear transmission mechanism and the power input member of the second gear transmission mechanism.
With the prime object of improving a transverse type automatic transmission of the abovementioned kind, there has also been proposed in U.S. patent application Ser. No. 425,257, filed on Sept. 28, 1982, and entitled "Transverse type automatic transmission with intermediate power transfer through lay shaft" an automatic transmission which includes a fluid torque converter and a first and a second gear transmission mechanism each of which has two coaxial drive members--a power input member and a power output member--and is selectable to any one of several speed ratios, wherein: rotational power is outputted from the fluid torque converter to the first gear transmission mechanism; the torque converter, and the first gear transmission mechanism including the power input and the power output members thereof, are all coaxial on a first axis; a through lay shaft extends along a second axis parallel to the first axis, and passes through the second gear transmission mechanism so as to support it, and is rotationally coupled to the power input member of the second gear transmission mechanism; a gear wheel rotationally coupled to the power output member of the first gear transmission mechanism transfers rotational power to a gear wheel meshed with it and fixed to the through lay shaft, which transfers this rotational power to the power input member of the second gear transmission mechanism; and a power output gear wheel is rotatably supported by the trough lay shaft and is rotationally coupled to the power output member of the second gear transmission mechanism.
These configurations of automatic transmission are satisfactory in minimizing the axial length of the transmission with an advantageous feature that the lay shaft assembly including the second gear transmission mechanism is supported by a through lay shaft which integrally extends over the entire axial length of the lay shaft assembly thereby providing an integrally stable and durable unit assembly for the combination of the lay shaft and the second gear transmission mechanism. However, in the configurations of automatic transmission of the above identified prior patent applications, the provision of the through lay shaft in the rotational power transmission system which includes a gear transmission mechanism and selectably provides a plurality of speed ratios inevitably requires a telescoped arrangement of an internal shaft element and an external hollow shaft element and also some related radially duplicated bearing arrangements, and therefore it raises a problem that it makes the configuration of the lay shaft assembly somewhat complicated and it also makes the assembly and disassembly procedures of the transmission delicate and difficult.